Causal relationships between type 2 diabetes, glycemic traits and keratoconus

PurposeThe relationship between diabetes mellitus and keratoconus remains controversial. This study aimed to assess the potential causal relationships among type 2 diabetes, glycemic traits, and the risk of keratoconus.MethodsWe used a two-sample Mendelian randomization (MR) design based on genome-wide association summary statistics. Fasting glucose, proinsulin levels, adiponectin, hemoglobin A1c (HbA1c) and type 2 diabetes with and without body mass index (BMI) adjustment were used as exposures and keratoconus was used as the outcome. MR analysis was performed using the inverse-variance weighted method, MR-Egger regression method, weighted-mode method, weighted median method and the MR-pleiotropy residual sum and outlier test (PRESSO).ResultsResults showed that genetically predicted lower fasting glucose were significantly associated with a higher risk of keratoconus [IVW: odds ratio (OR) = 0.382; 95% confidence interval (CI) = 0.261–0.560; p = 8.162 × 10−7]. Genetically predicted lower proinsulin levels were potentially linked to a higher risk of keratoconus (IVW: OR = 0.739; 95% CI = 0.568–0.963; p = 0.025). In addition, genetically predicted type 2 diabetes negatively correlated with keratoconus (IVW: BMI-unadjusted: OR = 0.869; 95% CI = 0.775–0.974, p = 0.016; BMI-adjusted: OR = 0.880, 95% CI = 0.789–0.982, p = 0.022). These associations were further corroborated by the evidence from all sensitivity analyses.ConclusionThese findings provide genetic evidence that higher fasting glucose levels are associated with a lower risk of keratoconus. However, further studies are required to confirmed this hypothesis and to understand the mechanisms underlying this putative causative relationship

Visual Psychophysics and Physiological Optics Age-Related Changes in the Anterior Segment Biometry During Accommodation

PURPOSE. We investigated the dynamic response of human accommodative elements as a function of age during accommodation using synchronized spectral domain optical coherence tomography devices (SD-OCT). METHODS. We enrolled 33 left eyes from 33 healthy subjects (age range, 20-39 years, 17 males and 16 females). Two SD-OCT devices were synchronized to simultaneously image the anterior segment through pupil and the ciliary muscle during 6.00 diopter (D) accommodation for approximately 3.7 seconds in two repeated measurements. The anterior segment parameters included the lens thickness (LT), radius of curvature of the lens anterior surface (LAC), maximum thickness of ciliary muscle (CMTMAX), and anterior length of the ciliary muscle (CMAL). A first-order exponential equation was used to fit the dynamic changes during accommodation. The age-related changes in the dynamic response and their relationship were calculated and compared. RESULTS. The amplitude (r ¼ À0.40 and 0.53 for LT and LAC, respectively) and peak velocity (r ¼ À0.65 and 0.71 for LT and LAC, respectively) of the changes in LT and LAC significantly decreased with age (P < 0.05), whereas the parameters of the ciliary muscle remained unchanged (P > 0.05), except for the peak velocity of the CMAL (r ¼ 0.44, P ¼ 0.01). The difference in the time constant between the lens reshaping (LT and LAC) and CMTMAX increased with age (r ¼ 0.46 and 0.57 for LT and LAC, respectively, P < 0.01). The changes in LT and LAC per millimeter of CMTMAX change decreased with age (r ¼ À0.52 and À0.34, respectively, P < 0.05). The ciliary muscle forward movement correlated with the lens deformation (r ¼ À0.35 and 0.40 for amplitude, while r ¼ 0.36 and 0.58 for time constant, respectively, P < 0.05). CONCLUSIONS. Age-related changes in the lens reshaping and ciliary muscle forward movement were found. Lens reshaping was much slower than the contraction of the ciliary muscle, especially in aging eyes, and this process required the ciliary muscle to contract more to reach a given response

Analysis of water film thickness on contact lens by reflectometry technique

We report the use of optical reflectometry technique for evaluation of water film on contact lens. The water film can be measured through the spectral dependent reflectance evaluation, which is carried out by illuminating the contact lens with a white light and collecting the returning light with an optical fiber coupled to a spectrometer. Water film thinning process has been observed on different soft contact lenses and minimum measurable thickness is about 0.85 m. The measurement is fast and accurate. The water film measurement can be valuable for contact lens design to improve its hydrophilic properties. The technique can be extended for the study of tear film dynamics in an eye

The Watery Eye

The surface of the eye needs to be wet constantly to ensure its integrity in maintaining ocular comfort, clear vision, and ocular health. This article presents new findings in the tear dynamics of the human eye, with an emphasis on the tear meniscus and tear film through the day and in response to punctual occlusion and wearing of contact lenses. Recent advances in imaging technique are briefly discussed

Micrometer-scale contact lens movements imaged by ultrahigh-resolution optical coherence tomography

To dynamically evaluate contact lens movement and ocular surface shape using ultrahigh-resolution and ultralong-scan-depth optical coherence tomography (OCT). Clinical research study of a laboratory technique. Four different types of soft contact lenses were tested on the left eye of 10 subjects (6 male and 4 female). Lens edges at primary gaze and temporal and nasal gazes were imaged by ultrahigh-resolution OCT. Excursion lag was obtained as the distance between the lens edge at primary gaze and immediately after the eye was quickly turned either nasally or temporally. The inferior lens edges were imaged continuously to track vertical movements during blinking. Ultralong-scan-depth OCT provided quantifiable images of the ocular surface, and the contour was acquired using custom software. Excursion lag at the horizontal meridian was 366 ± 134 μm at temporal gaze and 320 ± 137 μm at nasal gaze (P > .05). The lens uplift at the vertical meridian was 342 ± 155 μm after blinking. There were significant differences in horizontal lags and vertical movements among different lenses (P < .05). Horizontal lags were correlated with radii of curvatures and sagittal heights at 6-mm and 14-mm horizontal meridian (P < .05). The blink-induced lens uplift first lowered by 104 ± 8 μm, and then lifted 342 ± 155 μm after the blink. Ultrahigh-resolution and ultralong-scan-depth OCT can assess micrometer-scale lens movements and ocular surface contours. Both lens design and ocular surface shape affected lens movements

Upper and lower tear menisci after laser in situ keratomileusis

To determine upper and lower tear menisci using optical coherence tomography (OCT) in volunteers after laser in situ keratomileusis (LASIK) for myopia. Thirty-five eyes of 35 nonsurgical volunteers were evaluated. Twenty-eight eyes of 28 volunteers who underwent LASIK served as the study group. The height, area, and volume of the upper and lower tear menisci were obtained in the study group, using OCT before surgery, 1 week, 1 month, and 20 months after surgery. At each visit, Schirmer test (type I, without anesthesia), tear break-up time, and corneal fluorescein staining score were evaluated. OCT imaging was conducted in the nonsurgical group with the same settings. The lower tear meniscus volume at baseline were significantly smaller in the study group compared with the nonsurgical group (t test, P 0.05). The upper and lower tear menisci decreased up to 1 month after LASIK and recovered by 20 months. OCT is a useful tool for evaluating the tear system in a noninvasive manner

Thickness changes in the corneal epithelium and Bowman’s layer after overnight wear of silicone hydrogel contact lenses

Abstract Background To investigate thickness changes in the corneal epithelium and Bowman’s layer after overnight silicone hydrogel contact lens (CL) wear by using ultra-high resolution optical coherence tomography (UHROCT). Methods Eleven subjects without CL wearing history were recruited for this study. An UHROCT was used to measure the thickness of the epithelium (ET), Bowman’s layer (BT), stroma (ST), and total cornea (CCT) at the center of both eyes. A silicone hydrogel CL was inserted in the right eye of each subject, and the fellow non-CL wearing left eye served as the control. The lens was inserted at 9:30 pm and removed at 8:00 am the next morning. The subjects were evaluated at 9:00 pm (baseline), 9:30 pm (lens insertion), 10:00 pm (before sleep), 7:00 am (waking), 7:30 am, and 8:00 am (lens removal). Results Compared to the lens insertion level, the ET of the lens-wearing eye increased by 5.73% at eye opening (P = 0.001). The ET of the non-CL wearing eye and the BT in both eyes did not change after overnight CL wear. Compared to baseline, the CCT of the lens-wearing eye increased by 2.87% upon waking (P = 0.003) and recovered 30 min later (P = 0.555). In contrast, compared to baseline, the CCT of the non-CL wearing eye did not increase upon waking (P = 0.105). Conclusions By using UHROCT, we found that overnight CL wear induced different swelling responses in the various sublayers of the cornea. Trial registration Retrospectively registered. Registration number: ChiCTR1800015115. Registered 07 March 2018

Characterization of Soft Contact Lens Fitting Using Ultra-Long Scan Depth Optical Coherence Tomography

Objectives. To evaluate the centration and movement of soft contact lenses and to verify the repeatability of two repeated measurements of the lens centration and movement using ultra-long scan depth optical coherence tomography (UL-OCT). Methods. A 1-day Acuvue® Define™ lens was tested on both eyes of 10 subjects (5 males and 5 females; mean age, 31.6 years). The centration and blink-induced movement of the contact lens were measured using UL-OCT at 5 min and 30 min after insertion. The measurements were repeated once at each checkpoint. Results. Good repeatability was found in the lens centration and movement between the two repeated measurements at either checkpoint. The values of the lens movement were 0.457 ± 0.248 mm and 0.402 ± 0.229 mm at 5 min and decreased to 0.197 ± 0.065 mm and 0.211 ± 0.110 mm at 30 min after insertion for the right and left eyes, respectively (P<0.05). Conclusions. The custom-built UL-OCT presented good repeatability of centration and movement in Define lenses at 5 min and 30 min after insertion. Most of the lenses were centered temporal and inferior to the cornea during the first 30 min wearing period. Compared with 5 min after insertion, the lens was centered better and exhibited less movement at 30 min

Entire contact lens imaged in vivo and in vitro with spectral domain optical coherence tomography

OBJECTIVE: To demonstrate the capability of directly visualizing the entire ocular surface and the entire contact lens on the eye using spectral domain optical coherence tomography (SD-OCT). METHODS: A custom built, high speed and high resolution SD-OCT was developed with extended scan depth and width. The eye was imaged before and after wearing a toric soft contact lens (PureVision, Bausch & Lomb, Rochester, NY). A lubricant eye drop (Soothe, Bausch & Lomb) was instilled in the eye to enhance the image contrast on the lens. The same toric soft contact lens immersed in the contact lens solution was also imaged with a contrast enhancement medium (0.5% Intralipid). RESULTS: Cross-sectional OCT images of the entire ocular surface were acquired with high resolution 2048×2048 pixels. Quantitative surface height map of the ocular surface was obtained from a radial scan dataset containing 32 B-scans. With the contrast enhancement agent, the entire toric soft contact lens was clearly visualized both in vitro and on the eye. The surfaces of the lens were detected and used to generate the thickness maps of the soft contact lens. CONCLUSIONS: SD-OCT with extended scan depth and width is a promising tool for imaging the entire ocular surface shape and soft contact lenses. This successful demonstration suggests that the extended depth SD-OCT is effective in studying ocular surface shape and its interaction with a soft contact lens. The novel method is helpful for contact lens fitting evaluation and lens design

Characterization of Soft Contact Lens Edge Fitting Using Ultra-High Resolution and Ultra-Long Scan Depth Optical Coherence Tomography

The authors characterized the edge fitting of soft contact lenses and predicted mismatches between the lens and the ocular surface using UHR-OCT and UL-OCT. This technology may open new methods for lens design and fitting evaluation